Rear-projection display

ABSTRACT

Various embodiments related to rear-projection image display are disclosed. For example, one disclosed embodiment provides a projector for projecting an image and a screen configured to display the image. The screen comprises a filter layer having a light reception side and an image display side. The filter layer includes an array of trapezoidal transmissive elements and an array of trapezoidal absorption elements, where a wider base of each of the trapezoidal transmissive elements faces the light reception side of the filter layer, and where a wider base of each of the trapezoidal absorption elements faces the image display side of the filer layer.

BACKGROUND

Rear-projection display systems may be of many different sizes andconfigurations, and may vary according to any number of factors.Examples of such factors include, but are not limited to, display screenorientation, intended user viewing angle, optical system used forprojection, angle of incidence of light projected onto the displayscreen, etc.

Depending upon the optics used to deliver a projected image to a rearprojection screen, ghost images may interfere with a viewing experience.A ghost image appears on the display screen as an offset replica of theprojected image. A ghost image may be formed, for example, when aprojected image ray encounters an interface between media havingdiffering refractive indices. At such an interface, one portion of theimage ray may be refracted while another portion is reflected. Thereflected portion, or the ghost ray, may reflect off other surfaceswithin the projection system and thereby appear on the display screen.

SUMMARY

Accordingly, various embodiments are disclosed herein that relate torear-projection image display. For example, one disclosed embodimentprovides a rear-projection display system comprising a projector forprojecting an image and a screen configured to display the image. Thescreen comprises a filter layer having a light reception side and animage display side. The filter layer includes an array of trapezoidaltransmissive elements and an array of trapezoidal absorption elements,where a wider base of each of the trapezoidal transmissive elementsfaces the light reception side of the filter layer, and where a widerbase of each of the trapezoidal absorption elements faces the imagedisplay side of the filer layer.

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used to limit the scope of the claimed subject matter. Furthermore,the claimed subject matter is not limited to implementations that solveany or all disadvantages noted in any part of this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an embodiment of a rear-projection display system.

FIG. 2 shows an embodiment of an image display screen.

FIG. 3 shows a representative portion of an embodiment of a Fresnellens.

FIG. 4 shows a graphical representation of angular-dependent lighttransmission from two embodiments of rear projection display screens.

FIG. 5 shows another embodiment of a rear-projection display system.

FIG. 6 illustrates an embodiment of a lens sheet.

DETAILED DESCRIPTION

As mentioned above, a rear-projection display may be of many differentsizes and configurations. For example, in some embodiments, arear-projection display system may take the form of a surface computingsystem comprising a horizontally-oriented display screen configured todisplay images to one or more users seated or standing around thedisplay screen. The surface computing device also may be configured toreceive touch inputs made on the display screen.

Depending upon the use environment, the display screens of such surfacecomputing devices may be sizeable, and therefore may be subject todeformation due to gravity, users touching, leaning on or placing drinksand/or other objects on the screen, and other factors not ordinarilyencountered by vertically-oriented rear projection display screens.Further, a horizontally-oriented display screen also may have other useconstraints not ordinarily present for vertically-oriented displayscreens. For example, because viewers of a horizontal display screen maysit around the screen, the viewers may view the screen from the side,rather than from the front. Therefore, it may be desirable to direct agreater intensity of light toward the sides of the display screen.Further, the optical systems used to deliver an image to the displayscreen may produce ghost images with different characteristics thanthose produced in a vertically-oriented rear projection system.

Therefore, embodiments of rear-projection display screens are presentedherein that may help to resist mechanical deformation, reduce ghostimage presentation, and distribute light intensity for ahorizontally-oriented rear projection display system such as a surfacecomputing device. While disclosed herein in the context of ahorizontally-oriented rear projection display system, it will beunderstood that the embodiments described herein may be used in anyother suitable use environment, including, but not limited to,vertically-oriented displays and displays having other suitableorientations.

FIG. 1 shows an example embodiment of a rear-projection display system100 comprising an optical wedge 102 configured to deliver lightprojected by projector 104 to a display screen 106 via total internalreflection. The depicted optical wedge 102 comprises an internalreflector 108 configured to form a folded optical path within theoptical wedge 102, such that the entire surface of the optical wedge 102may be used for image projection. Rear-projection display system 100further comprises a controller 110 configured to control the display ofan image via projector 104.

Rear-projection display system 100 further comprises a vision-basedtouch-detection system configured to enable the detection of multipletemporally overlapping touch inputs. In the embodiment shown in FIG. 1,the vision-based touch detection system comprises an infrared lightsource configured to illuminate the display screen 106 with infraredlight, and one or more image capture devices 112 configured to capturean image of a backside of display screen 106 via infrared lightreflected from an object on display screen 106 into optical wedge 102.It will be appreciated that, in some embodiments, the image capturedevices may be configured to capture an image of a frontside of thedisplay screen based on one or more focusing characteristics of thevision-based touch detection system.

Any suitable light source may be used to illuminate the display screenwith infrared light. For example, in the depicted embodiment, aplurality of infrared light-emitting diodes 116 may be arranged alongone or more edges of the display screen to inject infrared light intothe display screen. Additionally or alternatively, some embodiments mayincorporate a light source to provide an infrared backlight forilluminating the display screen.

The light injected into the display screen may leak out of the displayscreen, thereby allowing the light to be reflected into the opticalwedge 102 by any objects on the display surface 114. While disclosedherein in the context of a horizontally-oriented display system, it willbe understood that an optical wedge also may be used to deliver aprojected image to a display screen having any other suitableorientation. Further, it will be understood that the display screenembodiments disclosed herein may be used in any other suitable useenvironment.

The optical system of rear-projection display system 100 includesvarious interfaces between materials of differing refractive indices(e.g. wedge/air interfaces, interfaces between any cladding layersdisposed on the wedge, etc.) that may cause some light to be reflectedat such interfaces. This reflected light may then reflect from otherinterfaces in the system back toward the display screen, thereby leadingto ghost images. Further, as light exits the optical wedge 102 ofrear-projection display system 100 at the critical angle for totalinternal reflection, such light arrives at display screen 106 at arelatively high angle of incidence relative to the display screennormal. This also may cause issues with ghost images. Therefore, displayscreen 106 may be configured to block such ghost images. FIG. 2illustrates an embodiment of display screen 106 in more detail, andillustrates the path taken through display screen by an example ray “A”of light projected by projector 104.

Display screen 106 includes a filter layer 202 for filtering undesiredlight, such as ambient light and ghost images; a lens sheet 204 forredirecting light received from the optical wedge 102 (or other suitablelight delivery system) toward a direction normal to a viewing surface ofdisplay screen 106; and a light diffuser 206 for diffusing lightreceived from the filter layer 202. It will be appreciated that thesizes of the various parts depicted in FIG. 2 are neither to scale norintended to represent any size relationships among those parts, butinstead are sized to clarify the arrangements and the locations of thedepicted parts.

Filter layer 202 includes light reception side 210 and an opposing imagedisplay side 212. Image display side 212 is positioned to face displaysurface 208 of display screen 106, while light reception side 210 ispositioned to receive projected light from lens sheet 204. Filter layer202 also includes an array of trapezoidal absorption elements 214interspersed with an array of trapezoidal transmissive elements 216 totransmit projected light to display surface 208 while filtering ghostimages from the light projected to display surface 208.

Filter layer 202 acts to filter ambient light incident at displaysurface 208 from the projection system that might otherwise lead toreflection of the ambient light back to display surface 208 with anaccompanying loss in contrast. Each transmissive element of the array oftrapezoidal transmissive elements 216 has a wider base 218 facing lightreception side 210 of filter layer 202 and a narrower base 220 facingimage display side 212 of filter layer 202.

Trapezoidal transmissive elements 216 are configured to have a highertransmittance than absorbance of one or more visible wavelengths oflight. In contrast, trapezoidal absorption elements 214 are configuredto have a higher absorbance than transmittance of one or more visiblewavelengths of light to absorb ambient light incident at display surface208 and to absorb ghost images formed elsewhere in the projectionsystem. Each absorptive element of the array of trapezoidal absorptionelements 214 has a wider base 222 facing image display side 212 offilter layer 202 and a narrower base 224 facing light reception side 210of filter layer 202.

Trapezoidal absorption elements 214 further may be configured to have ahigher transmittance of one or more wavelengths of infrared light thanof one or more wavelengths of visible light. For example, if lightsource 116 is configured to produce infrared light, the infrared lightproduced may be reflected by objects touching display surface 208 sothat display screen 106 is sensitive to a user touch, to an objectplaced on display surface 208, etc. Thus, if trapezoidal absorptionelements 214 have a higher transmittance of one or more wavelengths ofinfrared light than of one or more wavelengths of visible light,trapezoidal absorption elements will transmit a greater quantity ofreflected infrared light for capture by image capture device 112 whileabsorbing one or more wavelengths of visible light, which may reduce theoccurrence of ghost images formed by reflected ambient light. Further,in some embodiments, the trapezoidal absorption elements may beconfigured to have a higher transmittance than absorbance of one or morewavelengths of infrared light, providing a greater transmissionefficiency of infrared light.

Trapezoidal absorption elements 214 may have any suitable structure. Forexample, the trapezoidal absorption elements 214 may be formed from orotherwise include an ink, dye or pigment that absorbs light in thevisible spectrum while transmitting light in the infrared spectrum. Theink, dye or pigment may be incorporated into at least a portion of eachabsorptive element of the array of trapezoidal absorption elements 214;may be printed, coated, or adhered to either wider base 222 or narrowerbase 224 of each absorptive element of the array of trapezoidalabsorption elements 214; or may be incorporated into filter layer 202 inany other suitable manner. In other embodiments, the trapezoidalabsorption elements may comprise a multilayer dielectric filter, or anyother suitable filtering mechanism than an absorbing ink, dye orpigment.

The array of trapezoidal absorption elements 214 and the array oftrapezoidal transmissive elements 216 are arranged as a one-dimensional(1D) array in FIG. 2. It will be appreciated that the array oftrapezoidal absorption elements may be in any suitable arrangement. Forexample, in some embodiments where projected light is close totelecentric and where ghost image generation occurs in more than onedimension, a two-dimensional (2D) array of cone-shaped trapezoidalabsorption elements may be employed.

As mentioned above, FIG. 2 shows lens sheet 204 being spaced from filterlayer 202. Lens sheet 204 comprises a 2D Fresnel lens 226 forredirecting light received from the projector toward a direction normalto the surface of the display screen 106. Some embodiments of thedisplay screen may use a 1D turning film. For example, an embodimentused with an optical wedge may include a linear or a nearly-linearturning film in use cases where the projected light is nearlytelecentric.

In the depicted embodiment, lens sheet 204 also comprises a rigidmechanical strength layer 228 having a first side 230 and a second side232. Fresnel lens 226 is positioned to receive projected light from thesecond side of rigid mechanical strength layer 228 and to transmit theprojected light received to light reception side 210 of filter layer202. The Fresnel lens 226 may be connected to rigid mechanical strengthlayer 228 in any suitable manner. For example, the Fresnel lens 226 maybe bonded, fused, glued, etc. to rigid mechanical strength layer 228.

Rigid mechanical strength layer 228 comprises a mechanically rigidmaterial, providing mechanical support for display screen 106 to resistscreen bowing or sagging from user touches to display surface 208, fromobjects placed on display surface 208, from the weight of display screen106, etc. This may help to prevent damage to display screen 106 fromsuch factors, and also may help to preserve image quality, which maysuffer if display screen 106 deforms.

In some rear-projection display screens without such a mechanicalstrength layer, the back surface (i.e. the surface that faces away froma viewer) of a Fresnel lens sheet is roughened to avoid reflections thatcould lead to ghosting, as well as avoiding aliasing and/or Moiréeffects occurring between a projection image pixel pitch and a facetpitch of the Fresnel lens. However, the presence of the mechanicalstrength layer 228 increases a distance between such a roughened surfaceand the filter layer 202. Where the surface of the mechanical strengthlayer is roughened, the diffusion of light caused by the roughenedsurface may result in a portion of the projected light falling ontotransmissive absorption elements 214 in filter layer 202. This mayresult in reduced light transmission to display surface 208, display ofa blurry image at display surface 208, problems with vision-based touchdetection, etc.

Therefore, in some embodiments, second side 232 of rigid mechanicalstrength layer 228 may be smooth, rather than roughened, to reducediffusion of the projected image onto the trapezoidal absorptionelements 214. Further, an anti-reflective layer 234 may be disposed onsecond side 232 of rigid mechanical strength layer 228 to combat ghostimages that otherwise may be caused by reflection from the smoothsurface of rigid mechanical strength layer 228. Anti-reflective layer234 may comprise any suitable material or materials. For example, insome embodiments, the anti-reflective layer 234 may comprise amulti-layer dielectric anti-reflective structure.

As discussed above, light reception side 210 of filter layer 202 ispositioned to receive projected light exiting Fresnel lens 226, so thatambient light and ghost images are filtered from the projected images. Arepresentative portion 300 of an embodiment of a Fresnel lens from lenssheet 204 is shown in FIG. 3. Image ray A, shown entering base 302 ofFresnel lens portion 300, refracts in the lens before exiting at facet304 toward filter layer 202. Two ghost image rays that may arise fromthe optical wedge 102 depicted in FIG. 1 are also shown in FIG. 3. Oneray is referred to as “low-angle ghost ray” and the other is referred toas “high-angle ghost ray” based upon the angles relative to the displayscreen normal at which the ghost rays exit the Fresnel facet. Low-angleghost image ray G1 enters base 302 at the same entry point as image rayA, but at a different entry angle. Thus, low-angle ghost ray G1 isinternally reflected at facet 306 before being emitted at facet 304.

To address low-angle ghost image rays, some rear-projection displaysemploy a one-dimensional lenticular lens array (not shown) for directinglow-angle ghost image rays toward an array of absorbing filter elements.The filter elements include wavelength selective dyes or inks arrangedas absorbing stripes running parallel to the one-dimensional lenses ofthe lenticular array.

However, such a lenticular lens arrangement may be unsuitable foraddressing high-angle ghost image rays. Referring to FIG. 3, high-angleghost image ray G2 enters at a position on base 302 offset from theentry point of low-angle ghost image ray G1 and image ray A. High-angleghost image ray G2 is internally-reflected at facet 304 before beingemitted at facet 306. In light of the angle at which ray G2 is refractedby the Fresnel facet, the ray may pass between the absorbing stripes ofa lenticular-type filter. Thus, high-angle ghost image ray G2 may appearon a display surface of a display screen.

FIG. 4 shows a graphical comparison of angular-dependent lighttransmission from a display screen comprising a lenticular array withthe embodiment of FIG. 2. Lenticular lens transmission curve L exhibitsa low-angle main lobe transmission band 402 corresponding to image ray Aand a high-angle transmission band 404 corresponding to high-angle ghostray G2. In contrast, trapezoidal lens transmission curve T only exhibitsa low-angle transmission band 406 corresponding to image ray A. Thus, itwill be appreciated that a filter layer employing an array oftrapezoidal transmissive elements may be more suited to reducing ghostimages transmitted to a display surface than one utilizing a lenticularlens arrangement.

Display screen 106 may be subject to forces during ordinary use that bowthe filter layer 202 toward the Fresnel lens 226. For example, where thedisplay screen 106 is used as a screen for a horizontally-disposedsurface computing device, users may push against the screen withexcessive pressure when making touch inputs, when resting elbows on thescreen, etc. Where a one-dimensional lenticular array (not shown) isused as a filter, the “bumps” of the lenticular array may be positionedsufficiently close to the facets of the Fresnel lens 226 that the facetsmay scratch the lenticular array when excessive pressure is pushedagainst the display screen. However, the use of the trapezoidal array offilter layer 202 may help to avoid such problems. This is because thewider bases of trapezoidal transmissive elements 216 and the narrowerbases of the trapezoidal absorption elements 214 provide at least aportion of a planar surface 236 that faces Fresnel lens 226, and therebymay increase a closest distance between the filter layer 202 and Fresnellens 226 compared to the use of a rear-projection lenticular array.Moreover, a reduction in damage to facets of the Fresnel lens 226 may berealized by increasing a contact area between facets of the Fresnel lens226 and the planar surface 236 during a contact event between the twostructures. It will be understood that other embodiments may utilizesuch a lenticular array.

Display screen 106 also comprises light diffuser 206 for diffusing lightreceived from filter layer 202 and spreading light in a viewingdirection from light emission side 240 of light diffuser 206. In ahorizontally-oriented rear-projection display system, light diffuser 206may be a low-gain diffuser, configured to produce a Lambertian orsimilar low-gain distribution of light, thereby facilitating viewing ofan image on the screen from the screen sides, and also not directingexcessive optical power along the screen normal, where it is less likelyto be viewed. Light diffuser 206 may further be configured to have amatte finish to reduce specular reflection of ambient light from displaysurface 208. Alternatively, light diffuser 206 may be configured to havea glossy finish to provide an increased contrast ratio or to alter acolor intensity of the projected image.

Light diffuser 206 may be bonded to image display side 212 of filterlayer 202 on a first side of light diffuser 206. Display screen 106 mayfurther comprise a transparent durability layer 238 disposed on lightemission side 240 of light diffuser 206 to resist contact damage todisplay screen 106. The transparent durability layer 238 may help toresist scratches to the display surface 208 caused by a user's finger, astylus, or other object contacting the display surface 208. Thetransparent durability layer may comprise any suitable material, and maybe formed on light diffuser 206 in any suitable manner. Examples ofsuitable materials include, but are not limited to, suitably hardtransparent ceramic coatings, polymer coatings, etc.

FIG. 5 shows another example embodiment of a rear-projection displaysystem 500 that may utilize the display screen embodiments describedherein. Rear-projection display system comprises a projector 502configured to project an image, and a display screen 504 configured todisplay an image projected by projector 502. Projector 502 includes alight source such as lamp 506, light-emitting diode (LED) array, etc,and also includes an image source 508, such as a liquid crystal display(LCD), digital micromirror device (DMD), etc., for producing an image.In the embodiment of FIG. 5, one or more mirrors 510 are utilized toincrease an optical path length and image size of the image projected bythe projector 502, instead of an optical wedge 102, to provide imageconjugates between the image source 508 and the projected image of theimage source 508 at or near the display surface 520. Rear projectiondisplay system 500 further comprises a controller 512 configured tocontrol the display of an image via the projector.

The rear-projection display device 500 also comprises an image capturedevice 524 configured to capture an image of the backside of displayscreen 504. Image capture device 524 provides an image to electroniccontroller 512 for the detection of an object 522 on the display screen.It will be appreciated that, in some embodiments, the image capturedevice may be configured to capture an image of a frontside of thedisplay screen based on one or more focusing characteristics of thedisplay system.

An infrared light source 526 may be used to illuminate the backside ofthe display screen with infrared light to facilitate vision-based touchdetection. In other embodiments, a visible light source may be used.However, the use of infrared light, as opposed to visible light, forvision-based touch detection may help avoid washing out of the projectedimage.

Other embodiments of rear-projection display system 500 may utilizeother approaches to detect user touches or objects at display surface520 of display screen 504. For example, display surface 520 may includecapacitive or resistive touch sensor mechanisms (not illustrated)configured to communicate with electronic controller 512, an externalcomputing device, a network, etc.

FIG. 6 illustrates another embodiment of a lens sheet in which theFresnel lens and mechanical strength layer comprise a single layer ofmaterial. As such, lens sheet 600 is formed from a rigid sheet ofmaterial 602, and comprises a Fresnel lens 604 molded, embossed, orotherwise directly formed thereon to direct projected light to filterlayer 202. Lens sheet 600 further comprises a second side coated with ananti-reflective layer 606 to help prevent the generation of ghost imagesarising from the reflection of a projected image from the second side ofthe lens sheet. As elsewhere, it will be appreciated that the sizes ofthe various parts depicted in lens sheet 600 are neither to scale norintended to represent any size relationships among those parts, butinstead are sized to clarify the arrangements and locations of theparts.

It will be appreciated that, for some embodiments of rear-projectionsystems where incoming light has a high incidence angle with respect toa surface normal of the lens sheet, a portion of the light may bereflected from the lens sheet, causing ghost images to form. To addressthis in part, some embodiments may include a total internal reflection(TIR) Fresnel lens or a combination Fresnel-TIR Fresnel transition lensdisposed adjacent the second side of the lens sheet in place of and/orin addition to a Fresnel lens disposed on the first side of the lenssheet. In such situations, the anti-reflective layer described above maybe modified or omitted according to the embodiment of the displaysystem.

While disclosed herein in the context of specific example embodiments,it will be appreciated that the display screen embodiments describedherein are exemplary in nature, and that these specific embodiments orexamples are not to be considered in a limiting sense, because numerousvariations are possible. The subject matter of the present disclosureincludes all novel and nonobvious combinations and subcombinations ofthe various processes, systems and configurations, and other features,functions, acts, and/or properties disclosed herein, as well as any andall equivalents thereof.

1. A display screen, comprising: a lens sheet having a first sideconfigured as a Fresnel lens and a second side coated with ananti-reflective layer; and a filter layer positioned to receiveprojected light exiting the lens sheet, the filter layer comprising alight reception side spaced from the lens sheet, and a plurality oftransmissive elements and a plurality of absorption elements, each ofthe absorption elements being configured to have a higher transmittanceof one or more wavelengths of infrared light than of one or morewavelengths of visible light.
 2. The display screen of claim 1, whereinthe lens sheet is mechanically rigid.
 3. The display screen of claim 1,wherein the plurality of absorption elements and the plurality oftransmissive elements comprise a plurality of trapezoidal absorptionelements interspersed with a plurality of trapezoidal transmissiveelements.
 4. The display screen of claim 3, wherein a wider base of eachof the plurality of trapezoidal transmissive elements faces the lightreception side of the filter layer and forms at least a portion of aplanar surface of the light reception side of the filter layer.
 5. Thedisplay screen of claim 1, the display screen further comprising: animage display side of the filter layer located opposite to the lightreception side of the filter layer; a light diffuser for diffusing lightreceived from the filter layer bonded to the image display side of thefilter layer on a first side of the light diffuser; and a transparentdurability layer disposed on the light diffuser.